Copper(II) complexes of (<i>R</i>,<i>S</i>)-alpha-hydroxymethylornithine and its N^delta-benzoyl derivative

Complex formation between copper(II) and (R,S)-α-hydroxymethylornithine of (R,S)-Nα-benzoyl-α-hydroxymethylornithine was studied in aqueous solution by potentiometric and spectroscopic (electron paramagnetic resonance and electronic absorption) techniques. The results show that the α-hydroxymethyl derivatives of ornithine are coordinated through the alcoholic group to the copper(II) ion in basic solution. Deprotonation and coordination of the α-hydroxymethyl group occurs and yields species with the amino and/or carboxylato groups also bound to the metal ion

Can the alpha-hydroxymethylated amino acid residue influence the peptide binding ability towards copper(II) ions?

Complexing ability of tetrapeptides Phe– (R,S)HmR–Arg–Lys, Phe–(R)HmR–Arg–Lys and Phe–(R,S)HmO–Arg–Lys containing potential multi-donor systems provided by the novel amino acid α-hydroxymethylarginine or by α-hydroxymethylornithine has been investigated by potentiometry and the spectroscopic methods (EPR, UV-VIS and CD). Their complexes with copper(II) ions were compared with those of the parent peptides Phe–Ala–Ala–Lys, Phe–Ser–Ala–Lys, Phe–Arg–Arg–Lys and Phe–Orn–Arg–Lys. The significant enhancement of thermodynamic stability is observed for the 2N and 3N species. The CD and EPR spectra support square-planar geometry in 3N species formed at physiological pH. The distortion of the metal environment is induced through the bend conformation adopted by the peptide molecule. The Lys residue is the critical factor influencing this geometry distortion in the 3N species. However, the presence of a α-hydroxymethyl group affects the stability of the complexes, most likely by stabilizing conformations suitable for metal complexation